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Petrovic V.,Research and Technological Development Center | Rosado P.,Polytechnic University of Valencia | Torres R.,Polytechnic University of Valencia
International Journal of Production Research | Year: 2010

In this paper we present a simple and fast approach for MAT generation in discrete form. It is used for manufacturability analysis in the part modelling stage of injected parts. The method is a volume thinning method based on straight skeleton computation, modified and applied in 3D on B-rep models in STL. The volume thinning of the B-rep model is based on its boundary surfaces offset towards the model interior. The surfaces' offset is done with an adequately proposed offset distance which makes some of the non adjacent offset model surfaces overlap (they 'meet' in mid-surface or MAT). Offset surfaces are used to reconstruct the topology of a new B-rep model (offset model). Overlapping surfaces in the offset model are detected, separated and aggregated to MAT. For adequate MAT precision and adequate MAT radius function, we propose to treat B-rep model concave edges (vertices) as cylinders (spheres) of zero-radius and offset them in an adequate way. On these bases, we present an iterative algorithm in which MAT is constructed in an incremental way by consecutive volume thinning of the obtained offset models. MAT construction is finished when an empty offset model is obtained. An algorithm has been created and implemented in Visual C++. Some of the obtained results are presented in this paper. © 2010 Taylor & Francis. Source


Barrientos-Ramirez S.,University of Alicante | Barrientos-Ramirez S.,Research and Technological Development Center | Montes De Oca-Ramirez G.,University of Alicante | Ramos-Fernandez E.V.,University of Alicante | And 4 more authors.
Applied Catalysis A: General | Year: 2011

A parent activated carbon (C-0) was subjected to four different treatments: (i) heat treatment at 1273 K in Ar (C-1); (ii) heat treatment at 473 K in air (C-2); (iii) oxidation with H2O2 (C-3) and, (iv) oxidation with HNO3 (C-4). These materials were evaluated as supports of CuBr-[1,1,4,7,10,10-hexamethyltriethylenetetramine] (CuIBr-HMTETA), a catalyst for the Atom Transfer Radical Polymerization (ATRP) of methyl methacrylate (MMA) using methyl-α-bromophenylacetate (MBP) as radical initiator. The supported catalysts showed an adequate control of polymerization, evidenced by polydispersity indexes (PDI) falling in the range 1.13-1.55. The best performance was achieved when activated carbon was treated with nitric acid (C-4) and with air at 473 K (C-2). Some copper leaching was always detected. The catalysts were reused and an adequate polymerization control was obtained in subsequent runs. © 2011 Elsevier B.V. All rights reserved. Source


Barrientos-Ramirez S.,University of Alicante | Barrientos-Ramirez S.,Research and Technological Development Center | de Oca-Ramirez G.M.,University of Alicante | Sepulveda-Escribano A.,University of Alicante | And 3 more authors.
Catalysis Today | Year: 2010

Three activated carbons exhibiting different textural characteristics were considered as support for CuBr-HMTETA catalyst in the Atom Transfer Radical Polymerization (ATRP) of methyl methacrylate. The pore distribution of the activated carbons played an important role in the control of the polymerization reaction: polydispersity index always failed in the range 1.1-1.3. However, the accessibility of the catalyst to pores in the activated carbon was limited by pore size and growing polymer size. Catalyst located within the micropores of spherical carbon was isolated from the growing polymer chains during the polymerization reaction, which took place at the mesopores. Mesoporous structure of LMA F-12 carbon enhanced polymerization rate but control over the molecular weight distribution was decreased. A carbon with an adequate distribution of micro- and mesoporosity (RGC-30) provided a suitable balance between activation and deactivation processes involving Cu(I) and Cu(II) catalytic species, which resulted in the appropriate control of the molecular weight during the methyl methacrylate polymerization reaction. © 2009 Elsevier B.V. All rights reserved. Source


Barrientos-Ramirez S.,University of Alicante | Barrientos-Ramirez S.,Research and Technological Development Center | Oca-Ramirez G.M.D.,University of Alicante | Oca-Ramirez G.M.D.,Research and Technological Development Center | And 5 more authors.
Applied Catalysis A: General | Year: 2011

The grafting of natural halloysite nanotubes (HNT) with aminosilanes exhibiting two (DAS) and three (TAS) amino groups has been investigated and compared to the physisorption of both silanes on halloysite nanotubes. Halloysite nanotubes were used as solid support for the heterogeneous Atom Transfer Polymerization of methyl methacrylate (MMA) into poly(methylmethacrylate) (PMMA) using CuBr as catalyst. Silane grafted on the nanoclay acts both as a ligand that bonds to CuBr and as a catalyst for the heterogeneous MMA polymerization. Grafting of halloysite nanotubes with DAS produced a polymer with polydispersities similar to those produced by the physically adsorbed diaminosilane catalyst, but conversion percentages were lower and a poorer control over the polymerization reaction was achieved. Grafting of halloysite nanotubes with TAS had a detrimental effect on the control of the polymerization reaction and a loss of catalytic activity due to the immobilization of the copper catalyst. The best control over the polymerization of methyl methacrylate is achieved when the catalyst is not immobilized by covalent bond on the surface of halloysite nanotubes. Therefore, physysorption of the CuBr/aminosilane complex on the halloysite nanotubes provided better control on the polymerization reaction compared to the grafting of the aminosilanes on the halloysite nanotubes. © 2011 Elsevier B.V. Source

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